Moriond QCD 2001 Gianluca Cavoto - Roma 1
Charmless Hadronic B Decays at BaBar
XXXVI Rencontres de Moriond
March 17th-24th, 2001
Gianluca CavotoUniversità di Roma La Sapienza & INFN
on behalf of BaBar Collaboration
Moriond QCD 2001 Gianluca Cavoto - Roma 2
Charmless Decays
Preliminary Branching Fraction measurements ( and upper limit ) with BaBar at PEP-II (h+h-) (h+) (h+)
Data from 1999-2000 run• 20.7 fb-1 on-resonance
N((4S)) = 22.74 ±0.36 million
• 2.6 fb-1 off-resonance
Moriond QCD 2001 Gianluca Cavoto - Roma 3
Physics Target B mesons : dominant decay : b c (Vcb) Charmless decays:
Direct CP search Time-dependent CP asymmetry
sin(2), 0 sin(2) Theoretical model validation
penguin diagrams
Cabibbo-suppressed tree
diagrams
Vtb
Vtd,s
VubVud,s
ud
u
u
u
d
Moriond QCD 2001 Gianluca Cavoto - Roma 4
BaBar detectorDIRC (PID)
144 fused silica bars11000 PMs
1.5T solenoid
EMC6580 CsI(Tl) crystals
Drift Chamber40 axial/stereo layers
Instrumented Flux Returniron / RPCs (muon / neutral hadrons)
Silicon Vertex Tracker 5 double sided layers
e+
(3.1GeV)
e- (9GeV)
SVT: z resolution ~70 micronsTracking: (pT)/pT = 0.13% pT 0.45%
DIRC: K- separation > 3.4 for P<3.5GeVEMC: E/E = 1.33%E-1/4 2.1%
Moriond QCD 2001 Gianluca Cavoto - Roma 5
DIRCherenkov
C measurement
Detector of Internally Reflected Cherenkov light. 144 fused silica bars (1.7 cm thick)11000 PMTs, 25-50 p.e./particle,10 mrad single photon resolution
Pion-Kaon separation at high momenta
Moriond QCD 2001 Gianluca Cavoto - Roma 6
B Candidate selection
2*2beamES
*BpEm
*beam
* EEE B
Initial state kinematic constraint:
energy substitued (constrained) mass
Fully reconstructed decaysEfficiency (with daughter BF)
00,h+0,h+0,h+h: 10-45% ,3-
20%
K0 as KS to +-
K+K-
K*+ K+0,KS +
mES
signalsideband
energy difference
Moriond QCD 2001 Gianluca Cavoto - Roma 7
Composite particles
mass KS mass
Additional cuts:KS :decay time significance : photon cos(*, cluster lateral shape
4.3 MeV
loose Kaon PID requirementson daugheters
mass
8.5 MeV
< E > ~ 3 GeV
Moriond QCD 2001 Gianluca Cavoto - Roma 8
Background suppression
Background dominated by continuum quark-antiquark production (u,d,s,c)
cos(Th) = cosine of angle between thrust axes of B
and rest of the event Fisher discriminant:
Linear combination of event-shape variables
cos Th
Fisher signal
signal
background
background
Loose Cut on cos(Th) to suppress bkg
hh E sideband (dots) continuum hh MC (histo)
(dots) B- D0 (histo)hh MC
Jet-like topology
Moriond QCD 2001 9
Likelihood fit analysis Use an extended global likelihood fit
to extract different signal yields (NS) in each topology
mES, E, Fisher(cosTh), ( mass),
C
Independent control sample to study Probability Density Function for both BKG and SIG Gaussian 2.6 MeV
ARGUS function
B- Do- h+h- E sideband
Moriond QCD 2001 Gianluca Cavoto - Roma 10
Why critical?:
Separate channels with same decay topology
Use as control sample: D*+ D0
C - C (K) distribution for true aon
Critical Kaon ID
PDF in momentum bins
C
p
Moriond QCD 2001 Gianluca Cavoto - Roma 11
Systematic Uncertainties
Vary PDF parameters alternative PDF
Variation in yield
Other systematics (% variation on BF):
track finding efficiency: 1.2% per track
(S ) efficiency 5(4)% B meson counting 1.6%
Moriond QCD 2001 Gianluca Cavoto - Roma 12
B0
2 charged particles in the final state
cut-based analysisdistributions for consistency check
K
KK
Moriond QCD 2001 Gianluca Cavoto - Roma 13
B+ B0
KS
KS
KS to
ML fit results
Cut based analysis cross-checks
KS
Moriond QCD 2001 Gianluca Cavoto - Roma 14
B+
BB background investigated:
ML fit allows for component
< 9.0 (UL 90%CL)
Max likelihood fit projection
Moriond QCD 2001 Gianluca Cavoto - Roma 15
Max likelihood fit projection
Moriond QCD 2001 Gianluca Cavoto - Roma 16
Summary BaBar has recorded 20.7 fb-1 last year
Expect to collect additional ~30 fb-1 in 2001
Next targets : Direct CP asymmetry in these and other
channels Time-dependent CP asymmetry ( )